Telephone-exchange trunking system.



Fig. 1

E. A. mmmaim- TELEPHONE EXCHANGE TRUNKING SYSTEM, APPLICATION FILED 06T-UYWIO. flENEWED MAY HI. Hill.

Patented May7, 1918.

8 SHEETS-SHEET I- -IIIIIIIIIIIIIHI 'q d E. A. MELLINGER.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

APPLICATION FILED out. n. 1910. nzuzwso MAY 18. m1.

E. A. mmmsen. TELHHGNE EXCHANGE TRUNKING SYSTEM. APPLICATKON. FILED UCT.H, I910. RENEWED MAY I8. 911.

1,265,228. PatentedMayZlSB. l

3 SHEETS-HIE? I.

WITNESS a fivmzvroxa 197: TOR/vine.

UNITED STATES PATENT OFFICE.

EDWARD A. MELLINGER, OF CHICAGO, ILLINOIS, ASSIGNOR T0 AUTOMrQTIGELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE TRUNKING SYSTEM.

Specification of Letters Patent.

Patented May '7, 1918.

Application filed Octoberll, 1910, Serial No. 586.531. Renewed May 18,1917. Serial No. 189,578.

[0 all when; it may comma:

ie it known that l, Euwann A. MELLIN- onn, va citizen of the UnitedSlates of America, and resident of Chicago, Cook county, Illinois, haveinvented a certain new and useful Improvement in 'lclephonc-ExchangeTrunking Systems, of which the following is a specification].

My invention relates to telephone exchange systems of that kind in whichautomatic switches are employed for selecting trunks or other lines. Itrelates more particularly to systems in which non-numerical trunkingswitches, sometimes called line switches, are employed between first andsecond selectors, whereby the said switches are greater in number thanthe trunks lead ing therefrom. In such case it frequently happens thatthe trunks are all busy, and that a number of the switches, although idle, are for this reason not available for use. Suppose, for example,that all of the trunks leading from a certain switchboard become busy,there will then be a certain number of switches thereon that are idle,but which are not available for use, because they,oan-

not find any trunks which are idle. It becomes desirable. therefore,that some provision be made' for preventing selection of an idle switchthat is temporarily precluded from finding an idle trunk or other line.

The object of my invention is, therefore, to provide an improved arrangment wle e by, in a system in which certaii switches re greater innumber than the tru, "s leaning therefrom, the idle switches cannot besetlected, and in which no connection therewith can be made after andwhile the trunks leading therefrom. are all in use.

It is also an object to provide an improved construction and arrangementwhereby the simultaneous use of all the trunks leading from a certainswitchboard, leayin a certain number of switches that are idle butincapable ogt use, willserve automatically to prevent. connection withany of Another object isato provide'a system in which a. ,j urality: oftrunking switches are bya jmaster switch, and in which from saidswitches are'already in use, the said master switch thereby beingincapable of operation except when one or more of the trunks are idle.

A further object is to providea novel arrangement whereby' a guardingpotential will b established for one or more idle switches to preventconnection therewith whenever it shall occur that all of the trunks orlines leading from said switches are in use, as in such case a switch,although itself not in use, is incapable of finding a trunk orlinc whichis idle,-and its actuation will accomplish no useful purpose.

Another object is to provide a system in which non-numerical trunkingswitches or employed. between the first and second selectors, so thatthe second selectors are common to all of the subscribers, and in whichthe simultaneous use of all the trunks leading from a certain group ofnon-numerical trunking switches will serve automatically to temporarilyprevent all further connection with that group, and to divert the pre-;vented connection to some other group, as "will hereinafter more fullyappear.

It is also an object to provide certain details and features ofimprovement and eethbinations tending to increase the general efliciencyand serviceability of a telephone exchange system of this particularchar acter.

In the accompanying drawings Figs. 1 and 2 taken together showdiagrammatically a. complete circuit connection established between twosubstations A, and A of ditferent exchanges in a system involving theprinciples ofm invention.

At A (Fig. 1 thereis shown a subscribei"s three-wire automaticsubstation. By three-wire t e is meant; thatwtypa -in which a groanconnection'isf used at the substationfor operatin p ,Thepiid substationis connected means of tw'ciline co ductorstothefirst; ector 0. The firstsl ector O has access-Ito terminals-of trunks &

Fig. '2. The trunk lines leading from each level of the selector bankcontacts are distributcd among a number of groups of these non-numericalswitches, and these groups of non-nu1ne1icul switches are common to anumber of diil'crent groups of selector S\\ltlfll(fS.

Fig. 3 is a diagram showing how the trunk lines leading from one levelof a number of dillercnt groups of first selectors may be distributedamong a number of groups of sec ondary line switches, and showing howthere may be a larger number of secondary switches in each group thantrunk lines leading therefrom.

The plunger-s of the non-n1nnerical trunking switches such as the oneshown at; I) (Fig. 1) are all normally in locking engagewent with aplunger shaft. (not shown) which is controlled by the mechanism shown at1 1, usually called a master switch. This master switch E controls theplungcrs of tin; trunking; switches of the group of which the sir ch Dis a nien'il'ier in such a manner hat the are normally held directlyopposinan idle trunlr line leading to a repeater sot-l1 as the repeaterF.

The selector switch shown at H (Fig. 2) is similar to the selector (1(Fig. l). The selector H has access to trunks leading to connectors. oneof which is the connector shown at 'I. At A. and C there are shown asubstation and first selector similar to those shown at A and C,respectively. As herein represented, there are but two bat teries. withtheir positive terminals preferably grounded; but it will be understood,of course, that there may be any number, depending upon the conditionsto be met.

The substations may be of any suitable or approved type. As shown, thesubstation A comprises the usual receiver 2, switch hook 3, transmitterl, induction coil 5,1ingcr l, condenser '7 and release springs 8, 9 andit). which springs are momentarily forced into contact by the cam arm 11on the downward movement; of the switch book 3. Like the cam 11, thereare also secured to the hook 3 thcicarn arms 12 and 13, When the hook isin its lowest position the cam 12 serves to press the spring 14 intoengagement with the spring 15 and to allow the spring 16 to disengagethe-spring 17. When the hook is in its lowest position the cam 13 holdsthe around spring 18 away from the spring 19. The locking cam 20 servesto prevent the rlial hnot shown) from being rotated as long as thoreceiver is on the hook, and also prc vents the. springJB from engagingspring 19, afterthemeceivcr is removed from the hook, untilthe dial isturned. The impulse wheel 21. carrying; the so-called vertical teeth 22and rotary tooth 23. and the cam 24- are so curcly fastened to the shalt25, to which is also secured a dial (not; shown) provided.

with finger holes. As soon as the dial is rotated, the ram it permitsspring 17 to disengage spring ltf.

On the backward movement of the impulse wheel the \crtical teeth 22force the spring 26 into engagement with the spring 27. Following thelast engagement of springs 2|; and ill, the rotary tooth 23 forces thespring 255 into engagement with spring The substation it. also suppliedwith a push button 30.

The substation A is connected to the selector U by means of the lineconductors 3i and 3'2. The selector (J of the general type disclosed inUnited States Letters lat (:Ilt #815,321, granted March 13, 1906, toKeith, Erickson ct Erickson. In general, it; conu'n'ises the Ha'uulahal't (not shown) carrying the wipers fill, ill and 35. This shaft hasa vertical motion controlled by the vertical magnet .J-tl and a rotarymotion con trolled by the rotary magnet 37. The private magnet 38controls the aide switch carry-- ing the wipers it), i ll and lid in theusual and well ltnonn manrnrr. The release oi the snitch mechanism isprovided for in the release magnet 43. The cut'oll relay 44 is for theinnnine of cutting oil the two line relays iii and i from battery.

The non-numerioal trunking switch shown at l) is of the general typedisclosed in British Patent No. 26,301 of 1906, and in the AmericanTelephone Journal of New York, N. Y., of June 6, I908, but is slightlymodified to operate in a system en'ibodying the principles of myinvention. it comrises the usual plunger (not shown) attached to theplunger arm 47. This plnn ger arm is at racted upon the energization ofthe magnet 48 to force the said plunger into a bank of trunk terminalsconsisting of a. plurality of sets of springs. The said plunger lltlt'ththe springs 49, 51, {ti'lfllld 55 into itllilitfl ilositi' with thesprings 50, :32, 5 and be, respectively. As the plunger is attracted theepring 535 is shifted out. of engagement with the sprinc 57 and intoengagement with the spring 5%).

The master switch l) is of the general type disclosed in the aforesaidBritish patent and Telephone Journal. The master switch I) comprises theratchet wheel 60 to the shaft of which there is also secured the notchedwheel 61. This notched wheel is usually constructed of fiber or somegood insulating material. The ratchet wheelifitl is capable of beingrotated upon the attraction of the armature 62 by the motor magnet (33.The switch also comprises the bank a consisting; of the individualsegments 64. 126, etc, and the. common segment 65. There is also a wiper66 secured to the pin ger shaft which is used to always keep som *one ofthe individual contacts in electrical conncetion with the common segment65. There names are a number of relays 67, 68 and 69, one of which isconnected to each of the individual segments of the master switch bank.There are also the operating relays 70, 71 and 72 and lamp 73 used inconnection with the master switch.

The repeater shown at F, as before stated,

exchange. It consists essentially of the two line relays 74 and 75 andthe differentiallywound double-wound relay 76. There is also a relay 77,the function of which will be explained later.

The selector shown at H. Fig. 2, is quite similar to that shown at C.Fig. 1, but unlike selector C it has no cut-oil" relay.

The connector shown at I is of the general type disclosed in UnitedStates Letters Patout No. 815,176, granted March .13, 1906, to Keith,Erickson & Erickson. It, like the selectors l and H, comprises a shaftand shaft wipers 78, 79 and 80, the vertical motion of the shaft beingcontrolled by the vertical magnet 81 and the rotary motion by the rotarymagnet 82. v The private magnet 83 controls the side switch carrying thewipers 84, 85, 86 and 87. The release of the connector is provided forin the release magnet 88. The operation of the switch is controlled bythe calling subscriber through the medium of the two line relays 89 and90.

he connector is also provided with a ringer relay 91 and twodouble-wound relays 92 and 93. 1

As before stated, the substation A and first selector C are likesubstation A and selector C in Fig. 1.

Having given a general description of the apparatus involved in thesystem, I will now describe the operations of the apparatus when asubscriber at substation A, f stance, calls a subscriber in anotherexchange, subscriber at substation A, for example, whose number we willassume to be 2220. In making the call the subscriber at substation Aremoves the receiver from the hook, which permits the springs 14 and 15to disengage and springs 16 and 17 to engage. The disengagement of 5rings 14 and 15 opens the circuit of the he] s 6. The engagement ofsprings 16 and 17 has no particular function at this time. Thesubscriber, after having removed the receiver, rotates the dial, andconsequently the impulse wheel 21 and cam arm 24, forward in the usualmanner. As the cam arm is rotated upon the forward movement of the dial,it strikes the cam 20, which then allows the spring 1 8 to engage spring19. The cam 24 also breaks the engagement of springs 16 and 17.

s the subscriber wishes to call the digit 2,112 rotates the dial untiltwo of the vertical teeth 22 and the rotary tooth 23 are carried 22strike the cam 9.

,rotary magnet 37.

past the cams 94 and 95 on the springs 26 and 28. As soon as the dial isreleased, the impulse wheel rotates backward.

and force the spring 26 into contact with the spring 27. The engagementof these two springs closes an energizing circuit through the verticalline rclay -l5 of the selector (J. This circuit extends from ground Gthrough springs 18 and 19, springs 27 and 26, conductor 31, side switchwiper 40, line relay 4:) and springs 96 and 97 to battery lead 98,thence through battery B to ground G. The relay 45 energizes over Theteeth this circuit tr-close a circuit through the vertical magnet 36.This Cll'Cllll; extends from ground G through springs 99 and 100, 101and 102 and 98. As the springs 27 and 26 engage twice momentarily, thevertical magnet energizes twice to raise the shaft and shaft wipers twosteps opposite the second level of bank contacts. After the shaft hasbeen raised one or more steps, the arm 114 is lifted from spring 112,permitting it to engage spring 113, which puts a guarding ground ontothe connector private bank contact of the calling line in the banks ofall of the connectors that have access to said line. This is to preventthe substation A from being called while it is making a call. A momentafter the vertical impulses are sent in, the rota tooth 23 strikes thecam 95 on spring 28 and forces said spring against the ground spring 27.This closes a circuit extending from ground G through springs 18 and 19,springs 27 and 28, line conductor 32, side switch wi er 39, line rela 46and springs 103 and 97 to battery lead 98. The rotary line relay 46energizes once over this circuit and closes a circuit through theprivate mag net 38. This circuit extends from ground G through s. rings99 and magnet 38 to attery lead 98, thence through battery B to groundG. The private magnet thereupon energizes and denergizes, permitting theside switch to pass to second position. As soon as wiper 41 reachessecond position a circuit is closed through the through wiper 41,interand rotary magnet 37 to attery lead 98. The rotar magnet energizcsonce to rotate the sllaft and shaft wipers one step onto the terminalsof a trunk leading to the switch D. The rotary magnet also presses downthe private ma net armature and breaks its own circuit. f the firstcontact upon which the wipers are rotated is idle, the private magnetarmature will be released when the rotary ma t armature falls back,'andthe side switc V will thereby be allowed to pass to third position. If,however, the first; trunk is busy, theprivate from ground G ruptersprings 105 bank'contact upon which the private wiper 34 is rotated willhave upon it a. guarding This circuit extends magnet 36 to battery lead104 and private 38 to the battery lead 98. The relay 220 does notenergize over this circuit, but the private magnet does energize,thereby locking the side switch in the second position, and as soon asthe rotary magnet dei nergizes, it is energized again and thus acts inthe manner .of a buzzer to rotate the shaft, carrying wipers 33, 34 and35 to a contact that is not busy, at. which time the side switch 15permitted to pass to the tlnrd posltlon. As soon as the side switchwipers 39 and 40 reach the .third position, the line conductors areextended to the switch 1). wiper 1-3 to the third position puts aguardin; ground on the private bank contact of the trunk leading; to theswitch D in the hanks of all of the first selectors that have access tothe switch D. This circuit. extends from ground (11 through side switchwiper l2, relay 22!) to wiper 3t, thence. to all of said private bankcontacts. A circuit also extends over the circuit just traced to thewiper Ill, thence through magnet 48, springs 58 and 57, armature 10G,contact point. 107, armature 108, contact 109 and coil 71 to bat-- tery.The lnagi'tet 48 is energized over this circuit and attracts the dangerarm 4:7. As the spring 58 is shifted from spring 57 to spring fill-uponthe attraction of the plunger arm, the holding circuit for magnet 48 isshifted through resistance 111 to battery, As before stated, the plungerbeing thrust into the bank of springs 49 56 forces springs 49, 51. 53and into engagement with springs 50, 52, 54.- and 56, respectively, T heengagement of the springs 4-9, 51. and 551 with springs 50, 52 and 56completes the trunk conductors to the repeater H. The engagement ofsprings 53 and 54 closes a circult through the relays 67 and 70 inmultiple. The circuit through relay 70 extends from ground G througharmature 115, contact point 116, relay 70, common segment (35 of masterswitch bank a, wiper 66, individual segment 64 and springs5-.lr and 53to battery lead 98. The other circuit extends from ground Gr throughrelay 6? and springs 5-1 and 53 to battery lead 98. The energization ofrelay 67 places ground potential upon the oint 117 by means of armature118 engagmg point 119. The function of this ground potential will heexplained more fully later.

' magnet 63.

The relay 70 energizes over the circuit leeiore traced to closethecircuit'of the motor This circuit extends from ground Gr throughcontact 120, armature 108, contact 121, springs 122 and 123 and motormagnet 63 to battery lead 98. The

The pa ssing oil.

motor magnet attracts its armature, which rotates the ratchet wheel onestep. As soon as the ratchet wheel is rotated one step the spring! 12+which normally rests in a notch in the wheel (31 is forced. against thespring 1'35 and held in this engaged position until the spring 12% againengages a notch in the wheel 61. The attraction of the motor armaturealso breaks its own. circuit at springs 12-2 and 1523 and the armaturefalls back, but as the circuit is now closed at springs 121 and 125, itin'nnediately attracted again. Thus it operates in the manner of a.buzzer to rotate the ratchet wheel until the spring 12% engages the nextnotch. By means of a suitable mechanical arrangement the rotary motionof the ratchet wheel is imparted to the plunger shaft, giving saidplunger shaft an oscillatory motion to move the plungers which are inlocking engagement therewith back and forth in front of the banks oftrunk terminals. The notched wheel 61 is so constructwlv that every timethe spring 121 et'tg'ages a. notch the pioneers stand directly oppositethe terminals of a trunk conductor leading to a repeater l Had the nextt'runlr after the one last put in use been busy, the Contact; 126 wouldhave guarding potential upon it, which, when the wiper 6S engaged saidcontact, would complete a circuit through the relay 70, which wouldenergize the motor n'iagnet again and thus would more the plungers tothe next trunk.

In case all of the trunks leading from the roop of switches of which theswitch D is a member are lousy, the relays 67, G8, 69, etc, will all beenergized in the manner before described, at which time a circuit willhe closed through. the relay 72. This circuit extends from ground Gthrough contact point 119, armature 118, contact. 117, arinature 128,etc,, through the armatures of all relays 67, 68, G9, etc.,consecutively, through. the armature of the relay individual to the lasttrunk, thence through relay 72 to battery.' The relay 72 remainsenergized long as the trunks are all busy, The energization of the relay72 opens the circuit of the relay 70 at armature 115 and contact 116,

which in turn deenergizes and opens the motor magnet circuit, therebystopping the operation of the master switch. The energize,- tion of therelay 72 also closes a circuit through the lamp 73, and puts a guardingpotential on the selector private bank contacts of all of the trunklines leading to the switches that are controlled by the master switch Ethat are not in use. This circuit extends from ground G through contactpoint 127, armature 106, thence through springs 57 and 58 of all of theidle switches D, through magnet 48 and back over conductor 130 to saidprivate bank contacts. Thus when all the trunk lines leading from agroup of non numerical switches I) become .16 nection with a trunkleading to a different he operation of the repeater 1 bus i s masterswitch E is prevented from magnet 151, thereby stepping the side switchusel ess y rotating, even though all its bank to second position, wh chcloses the circuit contacts are provided with a guarding poof the rotormagnet 152 to rotate the shaft tential, and at the same time a guardingp and shaft wipers to the first idle trunk as- 5 tential is providedforall trunk lines leadln sumed'to be the trunk leading to the coninto tis group of non-numerical switches, neetor I. The side switch wiperspass to even though some of said trunks are not the third position andthus connect the trunk actually in use. This a calling line is prelines132 and 146 directly from the repeater vented from beingextended intoconnec- F to the connector I. The energization of 10 tion with anon-numerical switch D from relay 76 of the repeater F, as the lines arewhich no idle trunks are available to extend grounded at the substationA, serves to 0 en t e connection farther. When the selector t e circuitof the relay 77 to prevent the wipersencounter a trunk line which isthus ground impulse from going to the connector guarded, they arerotated past it into oonover both sides of the line. f I

Or he 80 group of non-n imerica'l switches. last two digits is the sameas it was for the he foregoing is the operation of the censecond digit.2. The connector I, upon retral oiiice.mechiinism upon the operation ofceiving the round impulses over the verti- 2. he subcal line as t 9third digit is called, operates 20 member at substation A now rotatesthe dial y means of magnet 81 to raise the shaft and 85 and 28. T dialis now released and perhe rotary impulse l1 iewise operates to 26 mittedto rotate backward, forcing spring step the side switch to secondposition. The 26 twice against the ground spring 27. The side switchwiper 87, in passing to the secthese two, springs sends two endposition, shifts the connection of the imground impulses through thevertical line pulse spring 110 from the vertical magnet rain 74 of therepeater F. Thisrcircuit ex- 81 to the rotary ma net 82. The switch is30 ten s from ground G throu 'h springs 18 now in position for thefourth and last di it and 19, springs 27 and 26, conductor 31, O. Thesubscriber at substation A turns the wiper 40, shaft wiper 33, springs49 and 50 dial until ten vertical teeth on the impulse 0 switch 1). linerelay 74 of repeater F and wheel have passed the impulse springs 26.upper winding of relay 76 to battery lead 98, The dial, upon beingreleased, rotates back- 35 thencethrough batteryBto groundG; The ward,as before described, grounding the relays 74 and 76 both energize twiceover vertical line ten times and the rotary line is circuit, therebysending two ground imonce. Therepeater repeats the impulses the pulsesover trunk conductor'132 to the secsame as before to close the circuitof the 0nd selector H. is circuit extends from connector line relay 89.The relay 89 now 40 ground G through springs 133 and 134, operates toclose the circuit extending from springs 135 and 136, conductor 132,side ground G" through springs 153 and 110,

switch wiper 137 and line relay 138 of sesprings 154 and 155, wiper 87and rotary lector H to battery lead 139, thence through magnet82 tobattery lead 139. The rotary 45 crates in the same manner as theseieetor the shaft wipers 78. 79 and 80 ten steps onto to raise theshaft and shaft wipers 140. 141 the lineof the called subscriber. I

and 142 opposite. the second level of bank ow comes the one rotaryimpiilse,'as contacts. As the rotary tooth 23 of the imheretoforeexplained, which energizes the pulse wheel 21 passes the cam 90 onspring rotary relay 90. The energization of this .50 28 1t forges saidspring into engagement relay again closesthecircuit of the private withspring 27, which closes a circuit magnet 83. This circuit extends fromthrough the rotary line relay 75 of the reground G,through springs 153and 156, pester. This circuit extends from ground magnet 83 and springs157 and 158 to batthrough springs 18 and 19. springs 27 tery'lead 139.The private magnet energizes 65 and 28, rotary line conductor 32, wipers39 and de 'e'nergizes, permitting theside switch and 35, bank springs 55and'56, relay .75, to pass to third position. The wipers 84 lowerwinding of relay 76 and springs 113' and 85, in the third position,connect the and 144 to battery lead 98, thence to batcalling subscriberwith the called siib- V B- scriber. T e wiper 86, in third position,

60 The relay 75 energizes to close a circuit closes a circuit fromground G through extending from ground G through springs wiper86,-shiift wi er 80, private bank eon- 33 and 134, springs 185 and145,springs 149 tact.159, ofl'-norma springs 160 and 161 and M14150,conductor 146, wiper 147 and relay cut-ofi relay 162 to battery. Thecut-off 1- to battery-lead 13.9. :The relay 148 enrelay is energized,thereby disconnectin $5 ergizes to close a circuit through the privatebattery ,froin' the line relays 163 and 10 which prevents substation Afrom calling while another substation has connection with its line.

A circuit also extends from the contact 159 to the. corre.-'spondinccontacts in the banks of all of the connectors that have ac cess to thecalled line, thus putting a guarding potential on the private bankcontacts, which prevents a third party from calling substation A whilesaid substation is being called.

The subscriber at substation A is now in position to ring the calledsubscriber. As soon. as the dial stops rotating, the subscriber atsubstation A presses the button 39, which forces spring 165 intoengagement; with spring 166. The engagement of these two springs closesa circuit. extending from ground G through springs 18 and 19, springs166 and 165, springs 17 and 16, con cluctor 31, wipers 1-0 and 33springs 49 and 50 and relays 71- and 76 of repeater F to battery lead98. The relays 7-1 and 76 encrgize as before and close a circuit throughthe relay 89 of the connector. This circuit ex tends from round G"through springs 137i and 134, springs 135 and 136, conductor 13:2,wipers 137 and 140, relay 89 and upper wind; ing of relay 93 to battery.The energizetion of relays 89 and 93 at this time closes a circuitthrough the ringer relay 91. This circuit extends from ground G throughsprings 153 and 11.9, springs 15-1 and 155, wiper 87, ringer relay 91and springs 167 and. 168 to battery lead 139. The ringer rolay energizesand by so doing disconnects the calling from the called line andconnects the ringing current generator with the line of the calledsubscriber. A circuit is now closed through the bells of the calledsubstation extending from one side of the gen crator R through springs169 and 179, wiper 85, shaft wiper 78, conductor 171. condenser 172,bells 173, springs 17 i and 175. conductor 176, wipers 79 and 81 andsprings 177 and 178 to the other side of the generator R. The subscriberat substation A, upon hearing, the signal removes the receiver from thehook. Upon the removal of the receiver from the hook at substation A.the called 186 and 168 to battery lead 139. The relay 92 energizes overthis circuit and shifts the spring 157 out; of engagement with thespring 158 and into engagement with the spring 187. This shifting ofthesprings provides an energizing circuit for the relay 77 of the repeaterF, said circuit extendin from ground Gr through the side switct wiper86, springs 187 and 157, lower winding of the relay 93 relay 90, thenceover the heavy conductor to the repeater F, through the springs 189 and190, relay 77, back over the heavy conductor to the connector relay S9and the upper winding of the relay 93 to battery lead 139. The current;in the two windings of the relay 93 have opposite effects, thuspermitting the armature to remain in its norrrial positioni The relay 77of the repeater is energized over the circuit just traced, therebydisconnecting the rotary impulse spring 145 from the trunk 146, and alsodisconnecting ground G" from the spring 135 and supplying talkingbattery current to the calling subscriber over a circuit extending fromground G through the springs 192 and H3, lower winding of the relay 76,relay 75, thence over the heavy con ductor to substation A, throughprimary winding of induction coil 5, transmitter 4, push button springs188 and 165, switch hook springs 17 and 16, back over the heavycoudoctor to repeater F, through relay 7-1 and upper winding of relay 76to l tcry. The relay 76, like the relay 93 of the connector, isditl'erentially wound and therefore does not energizeover the circuitjust traced. Thus both subscribers may now converse, it being evident,of course, that the voice-currents flow through the condensers 193 and194 of the repeater and condensers 195 and 196 of the connector.

The release of the apparatus used in the connection described isinitiated by the hanging up of the receiver at the calling substation.As the book 3 is lowered the cam arm 11 forces springs 8. 9 and 10momentarily into engagement, thereby groundin; both the vertical androtary lines simul taueously. Thus the relays 74, and 76 of the repeatermomentarily energize. The simultaneous energization of these threerelays closes a circuit through the relays 89, 99 and 93 of theconnector. The circuits thus closed are the same a's when the repeaterclosed the circuit of each line relay imlividually. The simultaneousenergization of the relays 89, 90 and 93 closes an energizing circuit.through the release magnet 88 of the connector in series with therelease relay 198 of the selector H. This circuit. extends from groundG" through side switch wiper 199, relay 198, private wiper 1-11; springs200 and 201, magnet 88 and springs 167 and 168 to battery. Theenergizing of magnet 88 restores the connoctor to normal position. -Therelay 198, u'pon energizing. closes a circuit extending from ground (1"through springs 202 and 202" and release magnet 203 to battery leadswitch 139. The release ma net attracts its armature, but does not reease the switch mechanism until the magnet deenergizes. turning now tothe repeater, the simultaneous cnergization of the relays 74, 75 and 76closes an energizing circuit through the release relay 220 of theselector C. This circuit extends from ground G through wiper 42, relay220, wiper 34, springs 51 and 52, conductor 204, springs 205 and 206,resistance 207 and springs 208 and 209 to the bat- 98. The resistance207 is low the relay 220 to be energized to close a circuit through therelease magnet 43. his circuit extends from ground G throu h springs 210and 211, and magnet 43, to attery. As soon as the release springs 8,9and 10 at the substation real: contact the line relays of the retionwhere the shaft and 159. As energizes for the the private magnetenergizes in manner.

' he energization of the private magnet this time, however, closes acircuit through c release ma his circuit extends ground at the privatebank contact through the private wiper 80, side wi er 86 (in secondposition), springs 212 and 213, magnet 88 and springs 16? he batterylead 139. The energizes and restores the hanism to normal position.

0W, as \the subscriber at substation A 7 presses the button to ring, asbefore, the vertical magnet 81 is energized over the same circuit coverwhich it was energized when the third digit was called. 3 soon as theshaft is raise one or more steps the arm 215 is also raised, whichallows the spring 217 to engage the spring- 216.- 'A busg signal callingsubscri er over from the battery lean secondary winding" 218 of the busy'signa chine ,springs 216*and 217,;side switch wiper 84 (m firstposition), ri ger springs 177 and 179, thence over the eavy ductor,including the condensers 196 and 4, to and through the substation A,back over the heavy conductor, including the more I numerical switchesthat are condenser 193 of the repeater, through the relays 89 and 93 tobattery. Upon hearing the busy signal the subscriber receiver on the allof the apparatus used in the connection in the manner hereinbeforedescribed.

From the foregoing it will be seen that means are provided forpreventing further selection of switches on a board after and while allof the trunks leadinlg therefrom are in use, and for diverting t eincoming calls to some other switchboard. ere are as many relays of by auarding potential is then established for al of the automatic switcheswhich are idle, the number of automatic switches bein greater than thenumber of trunks leading therefrom. In other words, when the trunks areall busy there is then an excess or surplus of switches, and means areprovided for preventing connection with the said excess or surplus, fordiverting the connection to some other switchboard. us the secondselectors are all common to the difl'erent subscribers, and at t e sametime the idle nonable to find an idle trunk are removed from the sphereof use, and are caused to remain m such condition until one that afterthe trunks f a certain guarding is established for the maining i laswitches, and the master switch prevented from operating to select atrunk-that is to sa it is so controlled that operate in any manner soonas a trunk is released, the excess 1 thenbeconie accessi 1e, and temaster switch is again operative o select idle trunks. It wi l pbservedthat the said master switch is ofthe type in which idle trunks areselected-aliead of the calls. In this way each calling subscriberobtains connection with a pres trunk, and at the sainctime causes themaster switch to select anot switches cona second sellector is conhertrunk for simfiar control over the connectors, which connectors areprovided with means for bridging the common battery a ross the, calledline. The repeaters. it will be seen, are also provided with means forbridging the talking battery across the trunk to sup ply talking batterycurrent to the calling: su i-station. The selectors and connectors areknown as numerical switches, and each one has motion first in one planeto select. a group, and then in another plane at. an angle UHEIBiLFtlIHt is to say, at an angle to the first planer-to find a line in theselected group. The selectors, of course, rotate automatical'ly tonuthmatically select an idle trunk in the prettermincd group. Eachconnector rotates under direct control of the subscriber to find thecalled line in the prc determined group.

A numerical switch is, of course, one that operates in accordance withsome digit of the called number. A non-numerical switch is one thatperforms a trunking operation without reference to the called number. Asshown. the non-numerical trunking switcl'ics are interposed between thefirst and second The first selector operates in ac cordanee with thefirst digit of the called numi'ei'. and the second selector operates inaccordance with the second digit thereof.

What I claim as my invention is:--

1. In a telephone system, a plurality of trunks, a plurality ofnon-numerical switches for automatically connecting with idle trunks.greater in number than said trunks, first selectors for automaticallyselecting idle switches in accordance with the first digit of the callednumber, and means serving anuse.

2. In a telephone system. a pluralitv of trunks. as many relays as thereare trunks. a plurality of switches for automatically selectinn idletrunks, greater in number than said trunks, means for automaticallyselecting idle switches, means for energizing, a relay each time a trunkis selected, and means whereby the energizing of all of said relaysserves to automatically prevent. further seizure of idle switches.

3. In a tele; gone system, a plurality of trunks, a plurality ofswitches for automatically connecting with idle trunks. greater innumber than said trunks, a set of relays for said trunks, onefor eachtrunk, relay mechanism adapted when energized to establish a idleswitches, a

relays of the set, and means for energizing a relay of said set eachtime a trunk is seized by a switch.

4. In a telephone system, ,a plurality of trunks, trunking switches,-amaster switch for selecting idle trunks for said switches,

switches after and elcctrically-controlled means automatica ly servingto prevent; actuation of said master switch after and while all of saidtrunks are in use. 4

5. in a telephone system, a plurality of truuks, uon-numerical trunkingswitches with which said trunks master switch for selecting idle trunksahead of the call for said trunking, switches, and means electricallycontrolled only by the =ii1mltaneoi.1s use of all said trunks to tom--porai'ily master switch.

6. In a tElQPliOl'lC system, a plurality of trunks, a plurality ofswitches for automatically connecting with idle trunks, greater innumber than said trunks, means for automatically selecting idleswitches, means serving automatically to prevent further seizure of idleswitches after and While the trunks are all in use, a repeater in eachtrunk, and a second selector at the end of each trunk, each repeateradapted to control the two sides of its trunk to control the sccandselector thereof.

T, In a telephone system, a plurality of trunks, a plurality ofnon-numerical switches for automatically connecting with idle trunks,greater in number than said trunks, first selectors for automaticallyselecting idle switches in accordance with the first digit of the callednumber, means serving automatically to prevent further seizure of idleand while the trunks are all in use, a repeater in each trunk, and asecond selector at the end of each trunk, each repeater adapted tocontrol the two sides of its trunk to control the second selectorthereof. H

8. In a telephone system, a plurality of trunks, as many relays as thereare trunks, a plurality of switches forautomatically selectino idletrunks, greater in munbcr than said trunks. means for auton'iaticallysclecb ing idle switches, means for energizing a relay each time a trunkis selected, means whereby the energizing of all. of said relaysservcslto auton'iatically prevent further seiz are of idle switches, arepeater in each trunk,

and a second selector at the end of each trunk. each repeater adapted tocontrol the two sides of its selector thereof.

9. In a telephone system, a plurality of trunks. switches forauton'iatically connecting with idle trunks, greater in number than saidtrunks, means for automatically selecting idle switches, means forautomatically establishing a guarding potential forall idle switchesafter and while the trunks are all in use, a. repeater in each. trunk,and a second selector at the end of each trunk. each repeater adapted tocontrol the two sides of its trunk to control the second selector ereof.

trunk to control the second prevent further actuation of said v Ill)ebanese 10. In a telephone system, a plurality of trunks, 3i: pluralityof switches for automatically connecting with idle trunks, greater innumber than said trunks, a set of relays for said trunks, one for eachtrunk, relay mechanism adapted when encr izcd to establish a guardingpotential for a l idle switches, a circuit for said mechanism controlledby all relays of the set, means for energizing a relay of said set eachtime a trunk is seized by a switch, a repeater in each trunk, and aselection of second selector at the end of each trunlr, each re'peateradapted to control the two sides of its trunk to control the secondselector thereof. a

11. In a telephone system, a plurality of switchboards, trunks leadingtherefrom, means for automatically selecting idle switches on saidboards, means automati cally serving when the trunks on any board areall in use to divert the automatic selection to some other board, arepeater in each trunk, and a second selector at the end of each trunk,each repeater adapted to control the two sides of its trunk to controlthe second selector thereof.

12. In, a. telephone system, a plurality of switchboards, trunks leadingtherefrom, switches on each board than 'the trunks leading therefrom,means for automatically selecting idle switches on said boards, meansfor preventing further idle switches on any board when all the trunksthereof are busy, there being trunk lines leading to said boards sodisposed that any attempted selection of an idle switch on a board whenall the trunks leading therefrom are busy will be diverted to anotherboard, a repeater in each trunk, and a second selector at the end ofeach trunk, each repeater adapted to control the two sides of its trunkto control the second selector thereof.

13. In a telephone system, a plurality of non-numerical trunkingswitchboards with trunks leading therefrom, means for extending callingconnections to said boards, devices rendered operative only by thesimultaneous use of all the trunks on any board to divert the calls toother boards, a repeater in each trunk, and a second selector at the endof e ch trunk, each repeater adapted to control the two sides of itstrunk to control the second selector thereof. Y

14. In a telephone system, a lurality of non-numerical trunking switchcards, the switches on any board being greater in numher than the trunksleading therefrom, means for automatically selecting idle switches onsaid boards, means for preventing further selection of, idle switches onany board when the other switches and all the trunks are in use, therebeing trunk lines leading to said boards so arranged that the preventedselection will greater in number said trunks,

be diverted to another each trunk, and a second selector at the end ofeach trunk, each repeater adapted to control the two sides of its trunkto control the second selector thereof.

15. In a telephone system, a plurality of trunks, trunkin switches, amaster switch for selecting id e trunks for said switches,electrically-controlled means automatically serving to prevent actuationof said master switch after and while. all of said trunks are in use, arepeater in each trunk, and a. second selector at the end of each trunk,each repeater adapted to control the two sides of its trunk to controlthe second selector thereof. 16. In a telephone system, a plurality oftrunks, non-numerical trunking switches with which said trunks aremultipled, a master switch for selecting idle trunks ahead of the callsfor said trunking switches, means electrically controlled only by thesimultaneous use of all said trunks to temporarily prevent furtheractuation of said master switch, a repeater in each trunk, and a. secondselector at the end of each trunk, each repeater adapted to control thetwo sides of its trunk to control the second selector thereof. 7

17. In a telephone system, trunks, a plurality of switches board, arepeater in a plurality of for automatically connecting with idletrunks, greater in number than said trunks, means for automaticallyselecting idle switches, means servingautomatically to prevent furtherseizure of idle switches after and while the trunks are all in use,telephone lines, and means for controlling the two sides of a. callingtelephone line to control said pwitchcs and extend the call to thecalled 18. In a telephone system, a plurality of trunks, a plurality ofnon-numerical switches for automatically connecting with idle trunks,greater in number than said trunks, first selectors for automaticallyselecting idle switches in acordance with the first digit of the callednumber, means serving automatically to prevent further seizure of idleswitches are all in use, telephone lines, and means for controlling thetwo sides of a calling telephone line to control said switches andextend the call to the called line.

19. In a telephone system, a. plurality of frunks, as many relays asthere are trunks, a plurality of switches forautomatically selectingidle trunks, greater in number than means for automatically selectingidle switches, means for energizing a relay each time a trunk isselected, means whereby the energizing of all of said relays serves toautomatically prevent 'further seizure of idle switches,,telephonelines, and means for controlling the two sides of a leading therefromare calling telephone line to control said switches and extend the callto the called line.

20. In a telephone system, a )lurality oi trunks, switches forautomatically connectinc with idle trunks, greater in number than saidtrunks, means for automatically select ing idle switches, means forautomatically establishing a guarding potential for all idle switchesafter and while the trunks are all in use, telephone lines, and meansfor controlling the two sides of a calling telephone line to controlsaid switches and extend the call to the called line.

21. In a telephone system, a plurality of trunks. a plurality o switchesfor automatically connecting with idle trunks,

- greater in number than said trunks, a set of relays for said trunks,

one for.each trunk, relay mechanism adapted to be energize to establisha guarding potential for all idle switches, a circuit for said mechanismcontrolled by all relays of the set, means for energizing a relay ofsaid set each time a trunk is seized by a switch, telephone lines, andmeans for controlling the two sides of a call ing telephone line tocontrol said switches and extend the call to the called line.

22. In a telephone system, a plurality of switchboards, trunks leadingtherefrom, means for automatically selecting idle switches on saidboards, means automatically serving when the trunks on any board are allin use to divert the automatic selection to some other board, telephonelines, and means for controlling the two sides of a. calling telephoneline to control sai switches and extend the call to the called line.

23. In a telephone system, a plurality of switchboards, trunks leadingtherefrom, switches on each board greater in number than the trunksleading therefrom, means for automatically selecting idle switches onsaid boards, means for preventing further selection of idle switches onany board when all the trunks thereof are busy, there being trunk linesleading to said boards so disosed that any attempted selection of anidle switch on a board when all the trunks busy will be diverted toanother board, telephone lines, and means for controlling the two sidesof a callin telephone line to control said switches an extend the callto the called line.

24. In a telephone system, a plurality of non-numerical trunkingswitchboards, the switches on any board being greater in number than thetrunks leading therefrom, means 'for automatically selecting idleswitches on said boards. means for prcventing further selection of idleswitches on any board when the other switches and all the trunks are inuse, there being trunk lines leading to said boards so arranged that theprevented selection will be diverted to another board, telephone lines,and means for controlling the two sides of a calling telephone line tocontrol said switches to extend the call to the called line.

25. In a telephone system, a plurality of trunks, trunking switches, amaster switch for selecting idle trunks for said switches,electricallv-controlled means automatically serving to prevent actuationof said master switch after and while all of said trunks are in use,telephone lines, and means for controlling the two sides of a callingtelephone line to control said switches to extend the call to the calledline.

26. In a telephone system, a plurality of trunks, non-numerical trunkingswitches with which said trunks are multipled, a master switch forselecting idle trunhs ahead of the calls for said trunking switches,means electrically controlled only by the simultaneous use of all saidtrunks to temporarily prevent further actuation of said master switch,telephone lines, and means for controlling the two sides of a callingtelephoife line to control said switches to extend the call to thecalled line.

27. In a telephone system, a plurality of trunks, a p urality ofnon-numerical switches for automatically connecting with idle trunks,greater in number than said trunks, first selectors for automaticallyselecting idle switches in accordance with the first digit of the callednumber, means serving automatically to preventfurther seizure of idleswitches after and while the trunks are all in use, telephone lines, acentral source of talking and operating current, and

connectors provided with means for bridging said source of currentacross any called telephone line.

28. In a telephone system, a plurality of trunks, as many relays asthere are trunks, a plurality of switches for automatically selectingidle trunks, reatcr in number than said trunks, means or automaticallyselectin;! idle switches, means for energizing a relay each time a trunkis selected, means wherebythe energizing of all of said relays servesto, automatically prevent further seizure'of idle switches, telephonelines, a central source of talking and operating current. and connectorsprovided with means for bridging said source of current across anycalled telephone line.

29. In a telephone system, a plurality of trunks, a plurality ofswitches for automatically connecting with idle trunks. greater innumber than said trunks, a set of relays for said trunks, one for eachtrunk, relay mechanism adapted when energized to establish a guardingpotential for all idle switches, a circuit for said mechanism controlledby all relays of the set, means for energizing a re lay of said set eachtime a trunk is seized by Ill image a switch, tele hone lines, a centralsource of talking and operating current, and conncctors provided withmeans for bridging said source of current across any called telephoneline. i

30, In a telephone s stem, a plurality of trunks, trunking switc es, amaster switch for selecting idle trunks for said switches,electrically-controlled means automatically serving to prevent actuationof said master switch after and while all of said trunks are in use,telephone lines, a central source of talking and operating current andconnectors provided with means for bridging said source of currentacross any called telephone I line,

31. In a telephone system, a plurality of trunks, non-numerical trunkingswitches with which said trunks are multipled, a master switch forselecting idle trunks ahead of the calls for said trunking switches,means electrically controlled only by the simultaneous use of all saidtrunks to temporarily prevent further actuation of said master switch,telephone lines, a central source a of talking and operating current,and cona said trunks, means nectors provided with means for bridgingsaid source of current across any called telephone line. I

32. In a telephone system, a plurality of trunks, a plurality ofswitches for automatically connecting with idle trunks, greater innumber than said trunks, means for automatically selecting idleswitches, means serving automatically to prevent further seizure of idleswitches after and while the trunks are all in use, telephone lines, are hater in each trunk, and a central sourceo and operating current,each repeater pro vided with means for bridging said source across thetrunk thereof .to supply talking current to the calling telephone line.

33. In a telephone system, a plurality of trunks, a plurality ofnon-numerical switches for automatically connecting with idle trunks,greater in number than said trunks, first selectors for automaticallyselecting idle switches in accordance with. the first digit of thecalled number, means serving autoly to prevent further seizure of idleswitches after and while the trunks are all in use, telephone lines, arepeater in each trunk, and a central source of talking and operatingcurrent, each repeater provided with means for bridging said sourceacross the trunk thereof to supply talking current to the callingtelephone line. 3 34. In a telephone system, a plurality of trunks, asmany relays as there are trunks, a plurality of switches forautomatically seecting idle trunks, greater in number than forautomatically selecting idle switches, means for energizing a relay eachtime a trunk is selected, means whereby the energizing of all of andrelays in number talking a l I 11 serves to automatically revent furtherseizure of idle switches, te ephone lines, a repeater in each trunk, andacentral source of talkin ando provi ed wit means for ridging saidsource across the trunk thereof to so ly talk' current to the callingtele hone me. 35. n a telephone system, a p urality of trunks, switchesfor automatically connecting with idle trunks greater in number thansaid trunks, means or automatically selecting idle switchesj-means forautomatically establish a guarding potential for all idle switches dfter and while the trunks are all in use, telephone lines, a repeater ineach and a central source of talking and operating current, eachrepeater provided with means for bridging said source across the trunkthereof to supply talking current to the calling telephone line.

36. Ina tele hone system, a plurality of trunks, a plum ity of switchesfor automaticdlly connecting with idle trunks, greater than said trunks,a set of relays for said trunks, one for each trunk, relay mechanismadapted when ener izcd to establish a guarding potential for all idleswitches, a circuit for said mechanism controlled by allrelays of theset, means for ener izing a relay of said set each time a tr is seizedby a switch telephone lines, a repeater in each trunk, and a centralsource of talking and operating current, each repeater provided withmeans for bridging said source across the trunk thereof to supplytalking current to the calling telephone 37. In a telephone system, aplurality of switchboards, trunks leading therefrom, means forautomatically selecting idle switches on said boards, meansautomatically serving when the trunks on any board are all in use todivert the automatic selection to some other board, telephone lines, arepeater in each trunk, and a central source of talkin and operatingcurrent, each repeater provi ed with means for bridging said sourceacross the trunk thereof to sup ly talking current to the callingtelephone line.

38 11 a telephone system, a plurality of switchhoards, trunks leadingtherefrom, switches on each board greater in number than the trunksleading therefrom, means for automatically selecting idle switches onsaid boards, means for preventing further selections of idle switches onany board when all the trunks thereof are busy, there being trunk linesleading to said boards so disposed that any attempted selection of anidle switch onie, board when all the trunks leading therefrom are busywill be diverted to another board, telephone lines, a repeater ineachtrlmk, and a central source of talking operating current eachrepeater provided with means for bridging said source crating currenteach repeater across the trunk thereof to sup ly talking current to thecalling telephone inc.

39. In a telephone system, a plurality of non-numerical trunkingswitchboards with trunks leading therefrom, means for extending callingconnections to said boards, devices rendered operative only by thesimultaneous use of all the trunks on any board to divert the calls toother boards, telephone lines, a re eater in each trunk, and a centralsource 0 talking and operating current, each repeater provided withmeans for bridgin said source across the trunk thereof to supp y talkingcurrent to the calling telephone line.

40. In a telephone system, a lurality of non-numerical trunking switchcards, the switches on any board being greater in number than the trunksleading therefrom, means for automatically selecting idle switches onsaid boards, means for preventing further selection of idle switches onany board when the other switches and all the trunks are in use, therebeing trunk lines leading to said boards so arranged that the preventedselection will be diverted to another board, telephone lines, a repeaterin each trunk, and a central source of talking and operating current,each repeater provided with means for bridging said source across thetrunk thereof to supply talking current to the calling telephone line.

41. In a telephone system, a plurality of trunks, trunking switches, amaster switch for selecting idle trunks for said switches,electrically-controlled means automatically serving to prevent actuationof said master switch after and while all of said trunks are in use,telephone lines, a repeater in each trunk, and a central source oftalking and operating current, each re eater provided with means forbridging said source across the trunk thereof to supply talking currentto the calling telephone line.

42. In a telephone system, a plurality of trunks, non-numerical trunkingswitches with which said trunks are multipled, a' master switch forselectin idle trunks ahead of the calls for said trunking switches,means electrically controlled only y the simultaneous use of all saidtrunks to temporarily prevent further actuation of said master switch,telephone lines, a repeater in each trunk, and a central source oitalkin and o crating current, each repeater provided wit means forbridging said source across the trunk thereof to supply talking currentto the calling telephone line.

43. In a. telephone system, trunks, a plurality of non-numericalswitches for automatically connecting with idle trunks, greater innumber than said trunks, first selectors for automatically selectingidle switches in accordance with the first digit a plurality of of thecalled number means serving automatically to prevent iurther seizure ofidle switches after and while the trunks are all in use, a numericalswitch for each trunk, and lines leading from each numerical switch,which lines are divided into groups, each numerical switch having motionin one plane to select a grou and then in another plane at an angle totile first plane to find a line in the selected group.

44. In a telephone system, a plurality of trunks, as many relays asthere are trunks, a plurality of switches for automatically selectingidle trunks, greater in number than said trunks, means for automaticallyselecting idle switches, means for ener izing a. relay each time a trunkis selecte means whereby the energizing of all of said relays serves toautomatically prevent further seizure of idle switches, a numericalswitch for each trunk, and lines leading from each numerical switch,which lines are divided into groups, each numerical switch havin motionin one plane to select a group an then in another plane at an angle tothe first plane to find a line in the selected group.

45. In a telephone system, a p rality of trunks, a plurality of switchesfor automatically connecting with idle trunks greater in number thansaid trunks, a set oi relays for said trunks, one for each trunk, relaymechanism adapted when energized to establish a guardin potential forall idle switches, a circuit tor said mechanism controlled by all relaysof the set, means for energizing a. relay of said set each time a trunkis seized by a switch, a numerical switch for each trunk and linesleading from each numerical switch, which lines are divided into groups,each numerical switch having motion in one plane to select a grou andthen in another plane at an angle to t e first plane to find a line inthe selected group.

46. In a telephone systemya plurality of trunks, trunking switches, a.master switch for selecting idle trunks for said switches,clectricallycontrolled means automatically serving to prevent actuationof said master switch after andwhile all of said trunks are in use, anumerical switch for each trunk, and lines leadingfrom each numericalswitch, which lines are divided into groups, each numerical switchhaving motion in one plane to select a group and then in another. planeat an angle to the first plane'to find a line in the selected group.

47. In a telephone stem, trunks, non-numerica with which said trunks aremultip ed, a master switch for selecting idle trunks ahead of the callsfor said trunking switches, means electrically c ntrolled only by thesimultaneous use of a plurality of all said trunks to tem- ,porarilyprevent further actuation of said trunking switches master switch, anumerical switch for each switch busy to the main switch, said meanstrunk, and lines leading from each numeriincluding a guarding potentialcircuit and cal switch, which lines are divided into a controllingmagnet in said auxiliary groups, each numerical switch having moswitch.a

t on in one plane to. select a roup and then 55. In a telephone system,a main switch,

in another lane at an angle to the'first an auxiliary switch accessiblethereto, a line plane to fin a line in-the selected group. accessible tosaid auxiliary switch, and 48. In a telephone system, a plurality of.means iormaking said line busy to the auxtrunks, as many relays asthere are trunks, a iliary switch and for makin said auxiliary pluralityof switches for automatically switch busy to the main switch, said meansectin'g idle trunks greater in number than including a guardingpotential circuit alot-, said trunks, a master switch for automatited tosaid line and a controlling magnet in cally selecting idle switches,means for enersaid auxiliary switch. gizing a relay each time a trunk isselected, 56. In a telephone system, a main switch, and means wherebythe energizing of all of a non-numerical auxiliary switch accessiblesaid relays serves to automatically prevent there 0, a line accessibleto said auxiliary further seizure of idle switches, and likeswitc meansfor making said line busy to wise prevents further operation of saidmasthe auxiliary switch and means for making ter switch. said auxiliaryswitch busy to said main 49. In a telephone system, a plurality ofswitch, said last means including the auxiltrunks, trunking switches, amaster switch iary switch. a 86 for selectin idle trunks for saidswitches, a 57. In a telephone system], a main switch,

e thereto, a line trunks, means for operating one of sai reaccessible tosaid auxiliary switch, means for lays whenever a trunk is seized, andcans making said line busy to the auxiliary controlled by theenergization of a plurality Switch and means for maklng said auxiliary90 of said relays for preventing actuation of switch busy to the mamswitch, said first said master switch. means including a guardingpotential cir- 50. In a telephone system, a main switch, cuit, said lastmeans comprlsing the auxila non-numerical auxiliary switch accessibleiary switch. thereto, a line accessible to said auxiliary 58. In atelephone system, a mam switch, switch, and means for making said linebusy an auxiliary switch accessible thereto, a line to the auxiliaryswitch and for making said accessible to said auxiliary switch, meansfor auxiliary switch busy to the main switch, making said line busy tothe auxiliary said means including the auxiliary switch. switch andmeans for making said auxiliary 51. In a telephone system, a mainswitch, switch busy to said main switch, said first 10o plurality orelays, one for each of said an auxiliary switch accessib an auxiliaryswitch accessible thereto, a line means com rising a guardin potentialcira cessible to said auxiliary switch, and cult allotte to said l1ne,sai last means inmeans for making said line busy to the auxcluding theauxiliary switch.

iliary switch and for making said auxiliary a 59. In a telephone system,a main switch, switch busy to the main switch, said means an auxiliaryswitch accessible thereto, a line including a guarding potential circuitd accessible to said auxiliary switch, means for the auxiliary switch.inking said line busy to the auxiliary 52. In a telephone system, a mainswitch, switch and meansfor making sa d auxiliary an auxiliary switchaccessible thereto, a. line swi ch busvto said main switch, saidsecondaccessible to said auxiliary switch, and means inc uding a guardingpotential cm means for making said line busy to the auxcuit and theauxiliary switch. iliary switch and for making said auxiliary 60. In atelephone system a main switch, switch busy to the main switch, saidmeans an auxiliary switch accesslb e thereto, a line including aguarding potential circuit allotaccessible to said auxillary switch,means for ted to said line and the auxiliary switch. making said linebusy to the aux l ary 116 53. In atelephone system, a main switch,switch and means for makingsaid auxiliary an auxiliary switch accessiblethereto, a line twitch busy to said main swatch, said first accessible,to said auxiliary switch, and and second meapscaelnnc mg aguard ng meansfor making said line busy to the aux-' potential circuit, the last meansincluding iliary switch and for making said auxiliary also the auxil aryswitch. switch busy to the main switch, said means 61. In a telephonesystem, a mam. switch, including a controlling magnet in said auxanauxiliary switch accessible thereto, a line iliary switch. I accessibleto said auxiliary swltch, means for 54. In a telephone system, a mainswitch, making said line busy to the aux l ary an auxiliary switchaccessible thereto, a line switch and means for makingsald auxlllary 12662. In a telephone system, a main switch, an auxiliary switch accessiblethereto, a line accessible to said auxiliary switch, means for makingsaid line busy to the auxiliary switch and means for making saidauxiliary switch busy to the main switch, said first means including aguarding potential circuit, said last means including a controllingmagnet in said auxiliary switch 63. In a telephone system, a mainswitch, an auxiliary switch accessible thereto, a line accessible tosaid auxiliary switch, means for making said line busy to the auxiliaryswitch and means for making said auxiliary switch busy to said mainswitch, said first means including a guarding potential circuit allotedto said line, said last means including a controlling magnet in saidauxiliary switch.

64. In a telephone system, a main switch, an auxiliary switch accessiblethereto, a line accessible to said auxiliary switch, means or makingsaid line busy to the auxiliary switch and means for making saidauxiliary switch busy to said main switch, said second means including aguarding potential circuit and a controlling magnet in said auxiliaryswitch.

65. In a telephone system, a main switch, an auxiliary switch accessiblethereto, line accessible to said auxiliary switch, means for making saidline busy to the auxiliary switch and means for making said auxiliaryswitch busy to said main switch, said second means including a guardingpotential cir cuit alloted to said auxiliary switch and a controllingmagnet in said auxiliary switch.

66. In a telephone system, a main switch, an auxiliary switch accessiblethereto, a line accessible to said auxiliary switch, means for makingsaid line busy to the auxiliary switch and means for making saidauxiliary switch busy to said main switch, said first and second meanseach including a guarding potential circuit, the last means includingalso a controlling magnet in said auxiliary switch.

67. In a telephone system, a main switch, an auxiliary switch accessiblethereto, a line acessible to said auxiliary switch, means for makingsaid line busy to the auxiliary switch and means for s itch busy to saidmain switch, said first means including a guarding otential circuitallotted to said line. an said second means including a guardingpotential circuit allotted to said auxiliary switch and a controllingmagnet in said auxiliaryswitch. 68. In a telephone system, a series ofmain switches, non-numerical auxiliary switches accessible thereto,lines accessible to said auxiliary switches, and means for making all ofsaid lines busy to the auxiliary switches and for making said auxiliaryswitches busy making said auxiliary.

to the series of main switches, said means including the auxiliaryswitches.

69. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches, andmeans for making all ofsaid lines busy to the auxiliary switches and formaking said auxiliary switches busy to the series of switches, saidmeans including guarding potential circuits and the auxiliary switches.

70. In a telephone system, a series of main switches, auxiliary switchesaccessible there to, lines accessible to said auxiliary switches, andmeans for making all of said lines busy to the auxiliary switches andfor making said auxiliary switches busy to the series of main switches,said means including guarding potential circuits allotted to said linesand the auxiliary switches.

71. In a telephone system, a series of main switches, non-numericalauxiliary switches accessible thereto, lines accessible to saidauxiliary switches, and mean for making all of said lines busy to thean? iary switches and for making said auxiliar switches busy to theseries of switches, sai means including magnets in said auxiliaryswitches.

7 2. In a telephone system, a series of main switches, auxiliaryswitches accessible thereto, lines accessible to said auxil y switches,and means for making all of in. lines busy to the auxiliary switches andfor making said auxiliary switches busy to the series 01 main switches,said means including guarding potential circuits andcontrolling magnetsin said auxiliary switches.

73. In a telephone system, switches, auxiliary switches accessiblethereto, lines accessible to said auxiliary switches, and means formaking all of said lines busy to the auxiliary switches and for makingsaid auxiliary switches busy to the series of main switches, said meansincluding guarding potential circuits allotted to said lines andcontrolling magnets in said auxiliary switches.

7 4. In a telephone system, a series of main switches, non-numericalauxiliary switches accessible thereto, lines accessible to saidauxiliary switches, means for making all of said lines busy to theauxiliary switches and means for making said auxiliary switches busy tosaid series of main switches, said last means including the'auxiliaiyswitches.

75. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary *itches,

- means for making all of said lines busyto the auxiliary switches andmeans for making said auxiliary switches busy to said seriesof mainswitches, said first means ineluding guarding potential circuits, saidlast means including the auxiliary switches.

7 6. In a. telephone system, a series of mai a series of main aromasswitches, auxiliary switches accesible thereto, lines accessible to saidauxiliary switches,

means for making all of said lines busy to the auxiliary switches andmeans for ma ng 1 switches.

77. In a telephone system, a series of main switches, to, linesaccessible to said auxiliary switches, means for making all of saidlines busy to the auxiliary said auxiliary switches busy to said se 'es0 main switches, said second means inc tidingguarding potential circuitsand the auxiliary switches.

78. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches, meansfor making all of said lines busy to the auxiliary switches and meansfor making said auxiliary switches busy to said series of main switches,said first means compris ing the guarding otential circuits, and saidsecond means inc uding guarding potential circuits, the last meansincluding also the auxiliary switches.

79. In a telephone system, a series of main switches, non-numericalauxiliary switches accessible thereto, lines accessible to saidauxiliary switches, means for making all of said lines busy to theauxiliary switches, and

means for making said auxiliary switches busy to said series of mainswitches, said.

last means including controlling magnets. in said auxiliary switches. a

80. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches, meansfor making all of said lines busy to the auxiliary switc ass, and meansfor making said auxiliaryswitchesbusy to said series of main switches,said first means ineluding guarding potential circuits, said last meansincluding controlling magnets in said auxiliary switches.

81. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches,

'means'jor making all of said lines busy to the auxiliary switches andmeans for making said auxiliary switches busy to said series of mainswitches, said first means including guarding potential circuitsallotted to said lines, said last means including controlling magnets insaid auxiliary switches.

$2. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches, meansfor making all of said lines busy to the auxiliary switches and meansfor making said auxiliary switches busy to said series of auxillaryswitches accessible thereswitches and means formakin main switches, saidsecond means including guarding potential circuits and controllingmagnets in said auxiliary switches.

83. In a telephone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches, meansfor making all of said lines busy to the auxiliary switches and meansfor making said auxiliary switches busy to said series 0 main switches,said second means includin guarding potential circuits allotted to saidauxiliary switches and controlling magnets in said auxiliary switches.

84. in a tele hone system, a series of main switches, auxiliary switchesaccessible thereto, lines accessible to said auxiliary switches, meansfor making all of said lines busy to the auxiliary switches and meansfor mak ing said auxiliar switches busy to said series of main switc es,said first means including guardin potential circuits and second meansinclu ing uarding potential circuits, the last means including alsocontrolling magnets in said auxiliary switches.

85. In a telephone system, a series of main switches, auxiliary switchesaccessible therc-- to, lines accessible to said auxiliary switches,means for making all of said lines busy to the auxiliary switches andmeans for makin said auxiliary switches busy to said series 0 mainswitches, said first means includin a uardin potential circuit allottedto each ine, an said second means including a guarding potential circuitallotted to cacl auxiliary switch and including also controlling magnetsin said auxiliary switches.

. 86. In a telephone system, a plurality of trunks, a plurality ofnon-numerical switches for automatically connecting with idle trunks,greater in number than said trunks, first selectors for automaticallyselecting an idle one of said switches in accordance with the firstdigit of the called number, and electromagnets and circuits servingautomatically to prevent further seizure of idle switches after andwhile the trunks are an in use.

87. In a telephone s trunks, a relay indivi ual to each trun a luralityof switches for automatically seacting idle trunks, reater in numberthan said trunks, electrica ly controlled means for automaticallyselecting idle switches, circuits for energizing a relay each time atrunk is selected, and electromagnets and circuits whereby the enerizing of all of said relays serves to automatically prevent fur-- therseizure of idle swi :hes.

88. In a tale hone system, a plurality of trunks, a plum ity of switchesfor automatically connectin with idle trunks greater in number than sa dtrunks, a set of relays for said trunks, one for each trunk andindividual thereto, relay mechanism adapted when energized to establisha guarding potential for all idle switches, a circuit for said mechanismcontrolled by all relays of the set, and circuits for energizin a relayof said set each time a trunk is seized by a switch.

89. In a telephone system, a plurality of trunks, trunkin switches, amaster switch for selecting id e trunks for said switches, a relay foreach trunk and individual thereto, and electromagnetic means controlledby said relays jointly to prevent actuation of said master switch afterand while all of said trunks are in use.

. 90. In a telephone system, a plurality of trunks, non-numericaltrunking switches with which said trunks are multipled, a master switchfor selectin idle trunks ahead of the calls for said trun ing switches,electromagneticmeans comprising a relay for each trunk and individualthereto controlled only by the simultaneous use of all of said trunks totemporarily prevent further actuation of said master switch.

91. Inv a telephone system, a plurality of groups of automatic switches,a group of trunk lines accessible to each group of switches, otherautomatic switches having access to said first switches, and meanscomprising trunk relays serving automatically when all the trunk linesin a particular group are busy to render the switches having access tosuch trunk lines busy also.

92. In a telephone system, .a plurality of groups of secondary automaticswitches, a group of trunk lines accessible to each group of secondaryswitches, groups of primary switches, the switches in each primary rouphaving access to switches in each 0 said secondary groups, and meanscomprisin a, relay for each trunk serving automatica ly when all thetrunk lines accessible to a particular group of secondarv switches arebusy for rendering such group of secondary switches busy to said primaryswitches.

93. In a telephone system, a plurality of groups of trunk selectingswitches, trunk lines leading into said groups, trunk lines leading outof said groups, means for selecting and seizing idle trunk lines leadinginto said groups, and means for preventing the seizure of an idle trunkleading into any particular group when all the trunk lines leading outof such group are busy, said last means comprising a set of chain relaysfor each group of outgoing trunks, and each chain comprising a relay foreach trunk of the group.

94. In a telephone system, a lurality of groups of secondary switches ana group of trunk lines accessible to each group, groups of primaryswitches, the switches of each primary group having access to a switchin each secondary group, and means comprising trunk relays and a circuitcontrolled thereby serving automatically when all the trunk lines of aparticular group are busy to render all the associated secondaryswitches busy also and to divert calls from said primary switch toanother secondary switch board.

Signed by me at Chicago, Cook county, Illinois, this 30 day of Sept,1910.

EDWARD A. MELLINGER.

Witnesses:

Eowano D. FALES, ARTHUR J. RAY.

